DESCRIPTION (Verbatim from the Applicant): Tendon injuries are a frequent and often devastating problem which primarily affects the young adult population. Despite a considerable volume of ongoing research, improvements in clinical outcome have been relatively limited over the past few decades. A better understanding of the mechanical events surrounding early recovery following tendon injury and control of mechanical factors during the rehabilitation program have thus far been the most effective interventions. This competitive renewal proposes to assess the gliding resistance, breaking strength, and histology of newer types of tendon repairs and the effect of new rehabilitation methods after tendon repair. In the initial funding period, using a partial tendon laceration model, we identified a number of determinants of friction following tendon repair and showed that increased friction is associated with poorer results in vivo. We found that the current high strength repairs are compromised by high friction costs, and we demonstrated that therapy which enhanced tendon gliding produced better final results in vivo, but at a cost of early repair gapping. We now propose to expand upon this work by studying newer repairs that may combine high strength and low friction, and rehabilitation methods which tailor the therapy to the mechanics of tendon gliding as these vary over time with tendon healing. Our hypothesis is that by optimizing tendon gliding during the rehabilitation period, both ultimate tendon motion and ultimate tendon strength can be improved. In order to study this hypothesis the following three Specific Aims are proposed: 1) to identify high strength, low friction repairs in a complete laceration canine model in vitro, 2) to characterize the short-term natural history of resistance to gliding and work of flexion in this model in vivo, and 3) to test in vivo the gliding characteristics, strength resistance to gap formation, and histology of a high-strength, low gliding resistance repair in this model, comparing an optimized rehabilitation model designed on the basis of the results in Specific Aim 2 with conventional therapy. Our earlier results, demonstrating the benefits of synergistic motion, have already been incorporated into clinical practice at our institution. We believe that the results of this study will also have rapid transference to the clinical arena.